1. Field of the Invention
The present invention relates generally to the study of multiple myeloma. More specifically, the present invention relates to the identification and validation of molecular determinants of myeloma bone disease through comparative global gene expression profiling and employment of the SCID-rab mouse model for primary myeloma. Further, this invention relates to methods of treatment of bone disease by stimulating bone formation and reducing bone loss via targeting molecular determinants identified by the global gene expression profiling.
2. Description of the Related Art
Multiple myeloma (MM) is a rare, yet incurable malignancy of terminally differentiated plasma cells (PC) that affects approximately 15,000 persons per year in the United States, and represents the second most common hematopoietic malignancy. Multiple myeloma represents 13% of all lymphoid malignancies in the white population and 31% of lymphoid malignancies in the black population. The malignant plasma cells home to and expand in the bone marrow causing anemia and immunosuppression due to loss of normal hematopoiesis.
Multiple myeloma is also associated with systemic osteoporosis and local bone destruction leading to debilitating bone pain and susceptibility to fractures, spinal cord compression and hypercalcemia. Myeloma is the only hematological malignancy consistently associated with lytic bone disease and local bone destruction is limited to areas adjacent to plasma cells, suggesting that the malignant plasma cells secrete factors that enhance osteoclast function and/or osteoblast anergy. The prevalence of bone disease varies with the presentation of myeloma, from smoldering myeloma, often without bone involvement, to solitary plasmacytoma, to diffused or focal multiple myeloma where systemic losses of bone mineral density or focal lytic bone lesions are seen in approximately 80% of patients.
In recent years, it has become evident that lytic bone disease is not only a consequence of myeloma, but that it is intricately involved in promoting disease progression. Change in bone turnover rates predicts clinical progression from monoclonal gammopathy of undetermined significance (MGUS) to overt myeloma by up to 3 years. While initially osteoclast and osteoblast activity are coupled, the coupling is lost with disease progression. Osteoclast activity remains increased and osteoblast activity is diminished, with lytic bone disease as the consequence. Studies in the 5T2 murine myeloma and the SCID-hu model for primary human myeloma demonstrated that inhibition of osteoclast activity is associated with inhibition of myeloma growth and reduction of myeloma tumor burden. These studies support reports that inhibition of bone resorption with bisphosphonates had an anti-myeloma effect.
Whereas the biology of osteoclasts in myeloma-associated lytic bone disease has been investigated intensively, little is known about the disease-associated changes in osteoblast activity and their underlying mechanisms. It has been suggested that in myeloma, the ability of mesenchymal stem cells to differentiate into the osteogenic lineage is impaired. However, the mechanisms responsible for such impairment have not been elucidated.
The Wnt signaling pathway is involved in both normal skeletogenesis and cancer related bone disease. The first link between Wnt signaling and human bone disease came from observations that inactivating mutations in the Wnt co-receptor, LRP5, causes the osteoporosis-pseudoglioma syndrome (OPPG) (Gong et al., 2001). The canonical Wnt signaling pathway is regulated by large number of antagonists, including the DKK family and secreted frizzled-related protein (SRFPs). To date, four Dkk proteins have been identified in mammals (Kawano and Kyota, 2003), among which Dkk1 and Dkk2 have been well characterized. Subsequently it was shown that mutations in LRP5 that causes a high bone mass phenotype were distinct from those seen in osteoporosis-pseudoglioma syndrome and prevented binding of Dickkopf-1 (DKK1), a soluble inhibitor of Wnt and high affinity ligand for LRP5 (Boyden et al., 2002; Little et al., 2002). DKK1, antagonizing the canonical Wnt pathway by binding to LRP5/6 and Kremen (Bafico et al., 2001; Mao et al., 2002; Mao et al., 2001), blocks maturation of osteoblasts and formation of mineralized matrix (Baron and Rawadi, 2007; van der Horst et al., 2005).
Additionally, over-expression of DKK1 in transgenic mice leads to decreased bone mass (Baron and Rawadi, 2007), while deletion of a single allele of DKK1 in mouse osteoblasts results in increased bone formation and bone mass (Morvan et al., 2006). The osteolytic prostate cancer line PC-3, when transfected with shRNA targeting DKK1, reverted to an osteoblastic phenotype. In addition, transfection of DKK1 into the osteoblastic prostate cancer cell line C4-2B, which normally induces a mix of osteoblastic and osteolytic lesions, caused the cells to develop osteolytic tumors in SCID mice. Thus, the role of DKK1 in promoting bone lesion development appears not to be limited to MM, but has also been indicated in prostate cancer.
In addition to inhibiting osteoblastogenesis, elevated DKK1 levels may enhance osteoclastogenesis. Thus, bone destruction, a cardinal feature of multiple myeloma (MM) may result from uncoupling of osteoclast and osteoblast activities (Bataille et al., 1991; Roodman, 2004; Taube et al., 1992). Osteoclasts are activated by binding of receptor activator of nuclear factor kappa B ligand (RANKL) (Anderson et al., 1997; Kong et al., 1999; Lacey et al., 1998) to its cognate receptor, RANK, while osteoprotegerin (OPG) (Simonet et al., 1997) (a soluble member of the tumor necrosis receptor super-family) acts as a naturally occurring decoy receptor that competes with RANK for binding of RANKL (Suda et al., 1999). MM cells likely stimulate expression of RANKL and suppress expression of OPG by osteoblasts or their progenitors (Giuliani et al., 2001; Pearse et al., 2001). Increased serum levels of RANKL and decreased levels of OPG have been associated with a poor prognosis in MM (Terpos et al., 2003). Restoring the RANKL/OPG imbalance by RANKL antagonist or recombinant OPG not only reduce MM-associated bone lesions but also halt disease progression in animal models (Pearse et al., 2001; Vanderkerken et al., 2003; Yaccoby et al., 2002; Oyajobi et al., 2001).
Mechanistically, regulation of osteoclastogenesis by osteoblast-derived OPG (Glass et al., 2005; Holmen et al., 2005; Jackson et al., 2005) and RANKL (Holmen et al., 2005; Galli et al., 2006; Spencer et al., 2006) involves Wnt signaling, a pathway that is regulated by a large number of antagonists, including members of the Dickkopf family (Morvan et al., 2006), the family of secreted frizzled-related protein (sRFPs) (Finch et al., 1997; Kawano and Kypta., 2003), and sclerostin (Semenov et al., 2005). Osteolytic bone lesion (OBL) in MM cells could be linked to DKK1 secretion by tumor cells (Tian et al., 2003; Giuliani et al., 2007; Haaber et al., 2007; Politou et al., 2006), inhibiting canonical Wnt in and differentiation of osteoblasts. Blocking DKK1 with a neutralizing antibody prevented MM-induced bone resorption in the SCID-rab model (Yaccoby et al., 2007). Although each appear to play an role in OBL, whether DKK1 might influence RANKL/OPG expression in myeloma has never been established.
The prior art is deficient in methods to diagnose and treat multiple myeloma bone diseases. Furthermore, the prior art is also deficient in understanding the disease-associated changes in osteoblast activity and the underlying mechanisms in multiple myeloma associated lytic bone diseases. The present invention fulfills this longstanding need and desire in the art.